1. Field of the Invention
The present invention relates to a method and an apparatus for recording or reproducing information on or from a recording medium, and more particularly to the method and apparatus which are used for general reproduction of information, communication or reproducing an information signal on a recording medium such as an optical disk or a magneto-optical disk.
2. Description of the Related Art
A typical system for recording or reproducing information known by the inventors of the present application is arranged to take the steps of individually reproducing timing signals in synchronism with a front edge and a rear edge of an information mark recorded on a recording medium such as an optical disk, reproducing the data corresponding to the front edge and the tail edge of the information mark in parallel, and synthesizing the reproduced data for the purpose of reproducing an original serial data. This system is disclosed in Japanese Patent Application Laying Open (KOKAI) No. 61-214278. As another system known by the inventors, it is possible to refer to "a system for detecting separate edges" used as a reproducing method, which is described in "Speeding up and increasing the capacity of an optical disk based on a pit-edge recording and MCAV recording system", Nationwide Learning Society of Electronic Information Communication, Autumn, 1990, SC-3-2.
Now, the deacription will be directed to the recording or reproducing system with a mark length on an optical disk. At first, an original information signal is modified into serial data consisting of 0 and 1 ranged in sequence. The original information signal may be directly used without modification. The modification is executed for the purpose of easily reproducing a bit-synchronization signal from a reproduction signal or suppressing waveform distortion of the reproduced signal, thereby enhancing reliability of information recording or reproduction. To achieve the purposes, it is possible to arrange the continuous bits "0" not to be too long or the bits "1" not to come too close to each other. Then, the following signals are utilized for this system in synchronism to the serial data. A recording signal is produced according to a light output of a recording laser beam. It indicates that the two states of the light output, that is, high and low, are alternately transited in synchronous to the serial data. At the bit "1" of the serial data, the state of the light output is changed. A plurality of marks are formed on the optical disk for indicating holy data is recorded when the recording laser beam is applied on the recording tracks at a constant speed for scanning. These marks are formed at predetermined intervals on the optical disk. Next, a reproduced signal is produced by taking the steps of scanning the optical disk as keeping the light output of the recording laser beam low for the purpose of avoiding breakage of information patterns on the optical medium, receiving the reflected light (or transparent light) from the medium, and converting the quantity of the received light into an electric signal. The tailing edge and the leading edge of the reproduced pulse signal correspond to the front edge and the rear edge of each mark. As another signal, a binary signal is produced by converting the waveform of the reproduced signal into a binary signal and inverting the binary signal. A bit-synchronization signal can be reproduced at the front edge and the rear edge of each mark.
It is preferable to make the binary signal equal to the recording signal. In actual, however, the length of the mark is made variable according to the change of a recording laser power, a recording laser beam diameter, or a sensitivity of a recording medium. In particular, as to the optical disk, a practically important issue is a variation of the mark length. If the mark length is variable, the binary signal is slipped on time against the bit-synchronization signal reproduced at the front edge and the rear edge of the mark. As a disadvantage, it is likely that the reproduced data becomes erroneous. To overcome the disadvantage, the foregoing systems have been proposed. However, these systems have another disadvantage as follows. Each of these systems is arranged to separate the serial data into the data for tile front edge of each mark and the data for the rear edge of the mark for the purpose of reproducing the data and to synthesize two kinds of parallel data into one serial data before reproducing meaningful data. Hence, these systems have difficulty in checking for the reproduced data by taking the steps of reproducing meaningful data in real time and recognizing it or in reproducing data accurately by feeding back the reproduced data into a data reproducing system. In addition, these systems are very costly.
Moreover, these systems are devised to allow a particular signal, re-synchronous signal, to be individually recognized from the data for the front edge or the data for the rear edge of each mark. This results in breaking the compatibility of an optical disk used in this system with an optical disk used in the systems proposed before the known systems, because the sector format of these systems is different from that of the hereto-proposed systems. In addition, a special reproducing circuit is required to be added. The foregoing systems have no availability in the field of an optical disk, for example and are very costly.